Thermosetting power compositions for the preparation of low-gloss coatings

ABSTRACT

The invention concerns powder thermosetting coating compositions comprising (a) an amorphous polyester containing carboxyl groups, rich in isophthalic acid and neopentylglycol, optionally branched with a polycarboxylic acid or a polyol containing at least three functional groups; (b) a semicrystalline polyester containing carboxyl groups prepared from one or several saturated aliphatic dicarboxylic acids with linear chain, and from a saturated aliphatic diol with linear or cyclic chain optionally branched with a polycarboxylic acid or with a polyol containing at least three functional groups, and having a melting point (Tm) of at least 40° C. and an acid value of 5 to 50 mg of KOH/g, and (c) a cross-linking agent. Said compositions are useful for preparing powder paints and varnishes providing excellent quality coatings whereof the brilliance measured at an angle of 60°, according to the ASTM D 523 standard is always less than 50%, that is half-gloss or matt coatings.

DESCRIPTION

[0001] The present invention relates to thermosetting powdercompositions comprising, as binder, a blend of an amorphous polyester,of a semicrystalline polyester and of a crosslinking agent, whichcompositions provide, by curing, low-gloss coatings, particularly mattcoatings.

[0002] The invention also relates to the use of these compositions forthe preparation of powder paints and varnishes which provide low-glosscoatings, as well as to the low-gloss coatings obtained from thesecompositions.

[0003] At the present time, thermosetting powder coating compositionsare widely employed as paints and varnishes in order to form durableprotective coatings on the most varied of objects. Powder coatingcompositions have many advantages over coating compositions that are inthe form of solutions in an organic solvent; on the one hand, the safetyand environmental problems caused by solvents are completely eliminatedand, on the other hand, whereas solvent-based coating compositions havethe drawback of only being able to be used partially—in certain types ofapplication, only 60% or less of the coating composition applied comesinto contact with the substrate and that part which does not come intocontact with the substrate cannot be recovered—power coatingcompositions are used 100%, given that only the powder in direct contactwith the substrate is retained by the latter, the excess powder being,in principle, entirely recoverable and reusable. This is why thesepowder compositions are preferred over coating compositions that are inthe form of solutions in an organic solvent.

[0004] Powder coating compositions generally contain a thermosettingorganic binder and, optionally, fillers, pigments, catalysts and variousadditives for tailoring their behaviour to their use.

[0005] These thermosetting powders are prepared in the following manner.The polyester or polyesters, the crosslinking agent, the optionalcatalyst, the pigments, the fillers and other additives are dry blendedat ambient temperature in the required proportions in order to obtain apowder paint or varnish. The blend thus obtained is put into an extruderin order to produce melt homogenization therein at a temperaturegenerally between 80 and 150° C. The blend leaving the extruder is leftto cool and then ground and screened in order to obtain a powder havingthe desired particle size of between 10 and 150 micrometres.

[0006] The powder paints and varnishes thus obtained are applied in amanner known per se by means of an electrostatic or triboelectric spraygun or using the technique of fluidized-bed deposition on the object tobe coated. The object thus coated is then heated in an oven where themelting and crosslinking of the binder is carried out at hightemperature.

[0007] The cured coatings obtained from thermosetting powder coatingcompositions must have a smooth, uniform and defect-free appearance andmust especially be free of any “orange peel”; they must have goodmechanical and chemical properties and good weatherability.

[0008] Furthermore, it is essential that the powder coating compositionsremain in the form of freely-flowing powders for a long enough periodafter their manufacture and their packaging, without reagglomeratingduring transportation and storage.

[0009] The thermosetting powder coating compositions commonly used andcommercially available contain, as binder, a blend of an amorphouspolyester containing carboxyl or hydroxyl groups having a glasstransition temperature (T_(g)) of between 45 and 80° C. with acrosslinking agent having functional groups capable of reacting with thecarboxyl or hydroxyl groups of the polyester.

[0010] The amorphous polyesters used in these compositions are thoseobtained from aromatic dicarboxylic acids, such as terephthalic acid orisophthalic acid, and optionally from aliphatic dicarboxylic acids, suchas adipic acid, and from various polyols, such as neopentylglycol,ethylene glycol, trimethylolpropane, etc.

[0011] These amorphous polyester-based compositions are storage-stableand produce coatings of excellent quality, inter alia a surface withoutany visible defects, and good mechanical properties. Among thesecompositions, amorphous polyester-based compositions rich in isophthalicacid provide coatings which are highly valued for their excellentperformance in outdoor exposure.

[0012] However, after curing, these amorphous polyester-basedcompositions provide coatings with a very high gloss. The gloss,measured at an angle of 600, according to the ASTM D 523 standard, isvery often greater than 90%.

[0013] Powder coating compositions whose binder contains asemicrystalline polyester have also already been proposed.

[0014] Thus, in European Patent 521,992, the binder proposed consists ofa blend of at least one semicrystalline polyester having an acid numberof 10 to 70 mg of KOH per gramme and of at least one amorphous polyesterhaving a glass transition temperature (T_(g)) of at least 30° C. and anacid number of 15 to 90 mg of KOH per gramme, with a crosslinking agentwhich may be an epoxidized compound, a compound containing activatedthiol or hydroxyl groups or an oxazoline.

[0015] Semicrystalline polyesters are characterized by one or more glasstransition temperatures (T_(g)) not exceeding 55° C. and a sharp meltingpoint of 50 to 200° C.

[0016] According to that patent, semicrystalline polyesters differ fromamorphous polyesters by the fact that semicrystalline polyesters have aheterogeneous morphology (they contain a mixture of phases), are opaqueand white in colour at ambient temperature, have a low melt viscosity,are more insoluble in organic solvents and have a very high structuralregularity. The semicrystalline polyesters described and used in theillustrative embodiments of that patent are those obtained bypolycondensation from dicarboxylic acids containing an aromatic oraliphatic ring, such as terephthalic acid and1,4-cyclohexanedicarboxylic acid, and from saturated aliphatic diolswith a linear chain, such as 1,6-hexanediol and 1,10-decanediol;furthermore, aliphatic dicarboxylic/acids with a linear chain, such asadipic acid, succinic acid or 1,12-dodecanedioic acid, are addedthereto. The amorphous polyesters used are polyesters containingcarboxyl groups usually employed in powder paints and varnishes; thesepolyesters may be rich in isophthalic acid for the purpose of obtainingoutdoor coatings having good weatherability.

[0017] According to that patent, the presence of the semicrystallinepolyester in the binder gives a coating having an excellent overallappearance, free of “orange peel”, and improved mechanical properties.

[0018] However, as shown in Table I at the end of the description ofthat patent, the coatings obtained from these compositions all have avery high gloss; the gloss, measured at an angle of 60°, according tothe ASTM D 523 standard, may vary between 82 and 87%.

[0019] U.S. Pat. No. 5,373,084 proposes thermosetting powder coatingcompositions which comprise, as binder, a blend of a particularsemicrystalline polyester, of an amorphous polyester and of acrosslinking agent. The particular semicrystalline polyesters proposedin that patent are those obtained by the esterification of a saturatedaliphatic dicarboxylic acid having a linear chain, mainly1,12-dodecanedioic acid, with a saturated aliphatic diol having a linearchain, mainly 1,6-hexanediol, and by optionally incorporating atrifunctional polyol, such as trimethylolpropane or glycerol, or atrifunctional polycarboxylic acid, such as trimellitic acid, in order toobtain branched polyesters. These semicrystalline polyesters have anacid number or hydroxyl number of approximately 20 to 120, preferablyapproximately 30 to 80 mg of KOH per gramme and a melting point of 40 to200° C., preferably 60 to 150° C. The amorphous polyesters used areamorphous polyesters containing conventional hydroxyl or carboxylgroups; these polyesters preferably have a glass transition, temperature(T_(g)) of at least 50° C and an acid number or hydroxyl number ofapproximately 25 to 80 mg of KOH per gramme. However, it will be notedthat the only amorphous polyesters described and used in that patent areamorphous polyesters rich in terephthalic acid, the acid constituent ofwhich contains at least 50 mol % of terephthalic acid and the alcoholconstituent of which contains at least 50 mol % of neopentylglycol andup to 10 mol % of trimethylolpropane; on the other hand, amorphouspolyesters rich in isophthalic acid are not mentioned in that patent.

[0020] The particular semicrystalline polyesters proposed in that patentact above all as reactive plasticizers. In the illustrative embodiments,it is shown that when the powder composition contains a small amount ofthe plasticizing semicrystalline polyester (at most 10% by weightcalculated with respect to the total weight of the amorphous andsemicrystalline polyesters), the composition provides coatings havingimproved properties, in this case a smooth appearance with little“orange peel”, a gloss measured at an angle of 60°, according to theASTM D 523 standard, of 96 to 97%, a good pencil hardness and excellentmechanical properties. However, just like European Patent 521,992mentioned above, U.S. Pat. No. 5,373,084 does not disclose thepossibility of obtaining coatings having a low gloss, for examplecoatings whose gloss measured at an angle of 60°, according to the ASTMD 523 standard, would be less than 50%.

[0021] However, there is an increasing need to be able to have availablethermosetting powder paints and varnishes which provide coatings havinga low gloss, such as, for example, satin or semi-gloss coatings or mattcoatings, which can be used inter alia for the coating of certainaccessories in the motor-vehicle industry, such as wheel rims, bumpers,etc., or else for the coating of metal beams and panels used in theconstruction industry.

[0022] Various methods have already been proposed for obtaining powderpaints and varnishes which provide coatings having a low gloss. However,experience has shown that it is difficult to produce a paint or varnishcapable of providing, under the usual extrusion and curing conditions, amatt or satin finish completely reliably and reproducibly. According toone of these methods, one or more special flatting agents, such assilica, talc, chalk and metal salts, are introduced into the powdercomposition in addition to the binder and the conventional pigments.However, the reduction in gloss is often insufficient and a pronounceddeterioration of the properties of the paint coatings is observed, suchas, for example a lack of adhesion to metal substrates. In order toremedy these drawbacks, European Patent 165,207 proposes to incorporatewaxes, for example a polyolefin wax, and metal salts (for example, zinc2-benzothiazolethiolate) into thermosetting powder compositions based onpolyesters terminated by carboxyl groups and on epoxidized compounds,such as triglycidyl isocyanurate. Likewise, U.S. Pat. No. 4,242,253proposes, as additives, calcium carbonate and finely dividedpolypropylene particles in order to produce low-gloss coatings. Thedrawback of this system is that the inorganic fillers, oftenincorporated in large amounts, may damage the extruders used forpreparing the powders and impair the desired surface appearance of thecoating obtained, which often has a rough and irregular appearance.Moreover, the waxes that are added easily migrate to the surface,thereby causing unacceptable variations in the degree of mattness of thecoating as it undergoes natural ageing. Furthermore, the fact of havingto add additional fillers in large amounts incurs an extra expense and,in itself, constitutes a drawback.

[0023] According to U.S. Pat. No. 3,842,035, it is known to produce amatt finish by using a coating composition obtained by dry blending twothermosetting powder compositions which were extruded separately. One ofthem is a slowly-curing composition (a long gel time) and the other arapidly-curing composition (a short gel time). Using this system, it ispossible, after curing, to obtain a matt coating without it beingnecessary to add a special matting agent to the powder composition. Themajor drawback of this system is that it requires dry blending largeamounts of already-formulated powders, something which is not easy todo, especially on an industrial scale. In addition, as this blendingcannot be carried out continuously, but only in batches of powder, it isnot easy to obtain the same degree of mattness in the coatings whengoing from one batch of powder to another. Finally, the powder which isrecovered after a first spraying operation and reused as paint cannothave the same composition as the powder had during the first sprayingoperation, thereby also resulting in a change in the degree of mattnessobtained.

[0024] There are also other systems that are intended to obtain mattcoatings in which two polymers of different nature or reactivity areused, as well as one or more crosslinking agents, so as to induce twodistinct crosslinking mechanisms, or two very different reaction rates.In these systems, the powder is prepared in a single step, unlike theprocess described in U.S. Pat. No. 3,842,035. It is then possible toproduce, in a single extrusion operation, a powder paint or varnishcapable of forming coatings of very low gloss.

[0025] By way of example, Japanese Patent Application 154,771/88describes a resin composition for a matt powder paint comprising a blendof a branched polyester containing hydroxyl groups having a highhydroxyl number and of another polyester containing hydroxyl groupshaving a lower hydroxyl number, in defined amounts, and a blockedisocyanate as crosslinking agent. This composition provides a mattcoating having good mechanical properties and good weatherability.International Patent Application WO 92/01756 describes powder coatingcompositions comprising a blend containing together (1) asemicrystalline polyester containing hydroxyl groups having a hydroxylnumber of 20 to 100, (2) an amorphous polyester containing hydroxylgroups having a hydroxyl number of 20 to 120, (3) an acrylic polymercontaining hydroxyl groups and (4) a blocked polyisocyanate ascrosslinking agent. The semicrystalline polyesters used are those whoseacid constituent contains from 85 to 95 mol % of terephthalic acid andfrom 5 to 15 mol % of 1,4-cyclohexanedicarboxylic acid and whose alcoholconstituent contains an aliphatic diol with a linear chain.

[0026] Using these compositions, low-gloss coatings (the gloss, measuredat an angle of 60°, according to the ASTM D 523 standard, does notexceed 35%) having good mechanical properties and good pencil hardnessare obtained. European Patent Application 366,608 describes powderpaints, obtained by extrusion, which provide matt coatings, but thesepaints contain two crosslinking agents. These powder paints contain anepoxy resin, particularly the diglycidylether of bisphenol A, apolycarboxylic acid, such as, for example,2,2,5,5-tetra(β-carboxyethyl)-cyclopentanone as the first crosslinkingagent, and a saturated polyester terminated by carboxyl groups,tolylbiguanide or dicyandiamide as the second crosslinking agent.

[0027] Finally, the use of active compounds in two different reactionsystems for producing matt coatings is described, for example, inEuropean Patent 104,424. That patent proposes the preparation of apowder by using only a single extrusion. This powder contains, asbinder, both a resin containing hydroxyl groups, such as a polyestercontaining hydroxyl groups, and a polyepoxidized compound, such astriglycidyl isocyanurate, and it contains a special crosslinking agentwhich, in its molecule, includes both carboxyl groups (in order to reactwith the epoxidized compound) and blocked isocyanate groups (in order toreact with the resin containing hydroxyl groups).

[0028] The main disadvantage of powder paints and varnishes obtainedfrom an extrusion described in the abovementioned patents is that theproperties of the powders obtained are very sensitive to variations inthe extrusion conditions, such as the extrusion temperature, the sheargradient, etc., and, since it is not easy to control these conditionsprecisely, it is difficult to always produce coatings having the samedegree of mattness from a well-defined composition. In particular, theproblem is to find a composition which, under the usual extrusionconditions, produces a low-gloss coating in a completely reliable andreproducible manner.

[0029] European Patent 551,064 proposes to solve this problem by usingthermosetting powder coating compositions which contain, as binder, ablend of a linear polyester containing carboxyl groups having an acidnumber of between 20 and 50 mg of KOH per gramme and of an acryliccopolymer containing glycidyl groups obtained from 5 to 30% by weight ofglycidyl acrylate or methacrylate and from 70 to 95% by weight of methylmethacrylate. These powder compositions make it possible to obtaincoatings of good quality having a very low gloss. This is because thegloss, measured at an angle of 60°, according to the ASTM D 523standard, is always less than 15%. Furthermore, these matt coatings havea smooth surface without any defects, good adhesion to metal surfacesand excellent weatherability. In addition, the properties of thesepowders are only slightly sensitive to variations in the extrusionconditions or are insensitive to them, which means that a definedcomposition practically always produces a matt coating havingsubstantially the same degree of mattness.

[0030] However, it has turned out that the matt coatings obtained fromthese compositions do not withstand mechanical deformations, given thatthe mechanical properties of these coatings are insufficient, inparticular the direct impact strength and reverse impact strength.

[0031] In conclusion, it may be seen that the various powdercompositions proposed hitherto for obtaining low-gloss coatings allstill have a certain number of drawbacks.

[0032] There therefore still remains a need to have availablethermosetting powder compositions capable of producing low-glosscoatings that do not have the defects of the compositions of the priorart.

[0033] According to the present invention, it has been surprisinglydiscovered that using, as binder, a blend of an amorphous polyestercontaining carboxyl groups, rich in isophthalic acid, and of asemicrystalline polyester containing carboxyl groups which is preparedmore particularly from a saturated aliphatic dicarboxylic acid with alinear chain and from a saturated aliphatic diol with a linear or cyclicchain, and of an appropriate crosslinking agent, it is possible toobtain thermosetting powder compositions which are capable of producinglow-gloss coatings in a completely reliable and reproducible manner andwhich have good mechanical properties and excellent weatherability.

[0034] The subject of the present invention is therefore thermosettingpowder coating compositions comprising, as binder, a blend of anamorphous polyester, of a semicrystalline polyester and of acrosslinking agent, which are characterized in that the bindercomprises:

[0035] (a) an amorphous polyester containing carboxyl groups, rich inisophthalic acid, prepared from an acid constituent comprising from 55to 100 mol % of isophthalic acid, from 0 to 45 mol % of at least onedicarboxylic acid other than isophthalic acid and from 0 to 10 mol % ofa polycarboxylic acid containing at least 3 carboxyl groups and from analcohol constituent comprising from 60 to 100 mol % of neopentylglycol,from 0 to 40 mol % of at least one dihydroxylated compound other thanneopentylglycol and from 0 to 10 mol % of a polyhydroxylated compoundcontaining at least 3 hydroxyl groups, the said amorphous polyesterhaving a glass transition temperature (T_(g)) of at least 50° C. and anacid number of 15 to 100 mg of KOH/g;

[0036] (b) a semicrystalline polyester containing carboxyl groupsprepared either

[0037] (b1) from a saturated aliphatic dicarboxylic acid with a linearchain having from 4 to 16 carbon atoms and from a saturated aliphaticdiol with a linear chain having from 2 to 16 carbon atoms and optionallyfrom a poly-carboxylic acid containing at least 3 carboxyl groups orfrom a polyol containing at least 3 hydroxyl groups, or

[0038] (b2) from 40 to 100 mol % of a saturated aliphatic dicarboxylicacid with a linear chain having from 10 to 16 carbon atoms and from 0 to60 mol % of an aliphatic dicarboxylic acid with a linear chain havingfrom 4 to 9 carbon atoms, calculated with respect to the total of thedicarboxylic acids, from a cycloaliphatic diol having from 3 to 16carbon atoms and optionally from a polycarboxylic acid having at least 3carboxyl groups or from a polyol having at least 3 hydroxyl groups,

[0039] the said semicrystalline polyesters having a melting point(T_(m)) of at least 40° C. and an acid number of 5 to 50 mg of KOH/g;and

[0040] (c) a crosslinking agent.

[0041] The amorphous polyesters containing carboxyl groups, rich inisophthalic acid, that are used in the compositions according to theinvention are polyesters having a high isophthalic acid content commonlyused in powder paint and varnish formulations for the production ofcoatings which exhibit excellent outdoor exposure performance.

[0042] According to the invention, the acid constituent of theseamorphous polyesters rich in isophthalic acid must contain at least 55mol % of isophthalic acid and it may even consist completely ofisophthalic acid (100 mol %).

[0043] The acid constituent of these amorphous polyesters mayfurthermore contain up to 45 mol % of an aromatic, aliphatic orcycloaliphatic dicarboxylic acid, other than isophthalic acid, such asterephthalic acid, phthalic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaricacid, maleic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid and mixtures of these compounds and upto 10 mol % of a polycarboxylic acid containing at least 3 carboxylgroups, such as trimellitic acid or pyromellitic acid. These acids maybe used in the form of the free acid or, if required, in the form of theanhydride, or else in the form of an ester with a lower aliphaticalcohol.

[0044] The alcohol constituent of these amorphous polyesters mustcontain at least 60 mol % of neopentylglycol and it may even consistentirely of neopentylglycol (100 mol %). The alcohol constituent ofthese amorphous polyesters may furthermore contain up to 40 mol % of analiphatic, cycloaliphatic or aromatic dihydroxylated compound, otherthan neopentylglycol, such as ethylene glycol, propylene glycol,1,4-butanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol,2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, hydrogenatedbisphenol A, neopentylglycol hydroxypivalate and mixtures of thesecompounds and up to 10 mol % of a polyhydroxylated compound containingat least 3 hydroxyl groups, such as trimethylolpropane,di-trimethylolpropane, pentaerythritol and mixtures thereof.

[0045] The amorphous polyesters containing carboxyl groups, rich inisophthalic acid, which may be used according to the invention have anacid number of 15 to 100 mg of KOH per gramme, preferably 30 to 70 mg ofKOH per gramme, and have a glass transition temperature (T_(g)) which isat least 50° C. so that the polyesters remain solid at the storagetemperature (20 to 50° C.), and which preferably varies from 50 to 80°C. The number-average molecular weight ({overscore (M)}_(n)) of theseamorphous polyesters is between 1100 and 11,500 and preferably between1600 and 8500. The melt viscosity (measured using a cone-and-plateviscometer according to the ASTM D 4287-88 standard) of these amorphouspolyesters may vary from 100 to 15,000 mPa.s at 200° C.

[0046] The semicrystalline polyesters containing carboxyl groups used inthe compositions according to the invention are semicrystallinepolyesters having a particular chemical constitution. They may be chosenfrom two types of polyesters, (b1) and (b2). The polyesters (b1) areprepared by polyesterification of a saturated aliphatic dicarboxylicacid with a linear chain having from 4 to 16 carbon atoms with asaturated aliphatic diol having from 2 to 16 carbon atoms. Preferably,these polyesters are linear, but branched polyesters may also be used inwhich the branching is introduced by means of a polycarboxylic acidcontaining at least 3 carboxyl groups, such as trimellitic acid orpyromellitic acid, or of a polyol such as trimethylolpropane,di-trimethylolpropane and pentaerythritol, these compounds being used inan amount ranging from 0 to 10 mol % with respect to all the monomerstogether.

[0047] Examples of saturated aliphatic dicarboxylic acids with a linearchain which may be used are succinic acid, glutaric acid, pimelic acid,suberic acid, azeleic acid, sebacic acid and 1,12-dodecanedioic acid.These acids may be used as a mixture, but they are preferably used bythemselves. 1,12-Dodecanedioic acid is the preferred acid. Examples ofsaturated aliphatic diols with a linear chain which may be used areethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol,1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol and1,16-hexadecanediol. These diols may be used as a mixture, but they arepreferably used by themselves. It is preferred to use 1,6-hexanediol.

[0048] The semicrystalline polyesters (b2) are prepared from 40 to 100mol % of a saturated aliphatic dicarboxylic acid with a linear chainhaving from 10 to 16 carbon atoms and from 0 to 60 mol % of a saturatedaliphatic dicarboxylic acid with a linear chain having from 4 to 9carbon atoms, calculated with respect to all of these dicarboxylic acidstogether. It is also possible to use from 40 to 95 mol % of the acidhaving from 10 to 16 carbon atoms and from 5 to 60 mol % of the acidhaving from 4 to 9 carbon atoms. The alcohol constituent of thesepolyesters is a cycloaliphatic diol having from 3 to 16 carbon atoms.Preferably, these polyesters are linear but it is also possible to usebranched polyesters in which the branching is introduced by means of apolycarboxylic acid containing at least 3 carboxyl groups, such astrimellitic acid or pyromellitic acid, or of a polyol such astrimethylolpropane, di-trimethylolpropane and pentaetythritol. Thesecompounds having at least 3 functions are used in an amount ranging from0 to 10 mol % with respect to all of the monomers involved in thepolyester composition.

[0049] Examples of saturated aliphatic dicarboxylic acids with a linearchain having from 10 to 16 carbon atoms are 1,10-decanedioic acid,1,11-undecanedioic acid, 1,12-dodecanedioic acid, 1,13-tridecanedioicacid, 1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid and1,16-hexadecanedioic acid. Preferably, 1,12-dodecanedioic acid is used,by itself or in a mixture.

[0050] Examples of saturated aliphatic dicarboxylic acids with a linearchain having from 4 to 9 carbon atoms which may be used are succinicacid, glutaric acid, pimelic acid, suberic acid and azelaic acid. Theseacids may be used in a mixture but they are preferably used bythemselves. Examples of cycloaliphatic diols having from 3 to 16 carbonatoms which may be used are 1,4-cyclohexanediol,1,4-cyclohexanedimethanol, hydrogenated bisphenol A,2,2,4,4-tetramethyl-1,3-cyclobutanediol and4,8-bis(hydroxymethyl)tricyclo[5.2.1.0^(2,6)]decane.

[0051] These diols may be used in a mixture, but they are preferablyused by themselves. It is preferred to use 1,4-cyclohexanediol orcyclohexanedimethanol.

[0052] The semicrystalline polyesters containing carboxyl groups whichmay be used according to the invention have an acid number of 5 to 50 mgof KOH per gramme, preferably 5 to 30 mg of KOH per gramme; preferably,these polyesters have a hydroxyl number which does not exceed 5 mg ofKOH per gramme.

[0053] These semicrystalline polyesters are solid substances at ambienttemperature, characterized by a melting point (T_(m)) of between 40 and90° C.

[0054] The number-average molecular weight ({overscore (M)}_(n)) ofthese semicrystalline polyesters is between 2200 and 25,000 andpreferably between 2800 and 11,220. The melt viscosity (measured using acone-and-plate viscometer according to the ASTM D 4287-88 standard) ofthese semicrystalline polyesters may vary from 50 mPa.s at 100° C. to10,000 mPa.s at 150° C.

[0055] It has been surprisingly found that only the thermosetting powdercompositions containing both an amorphous polyester rich in isophthalicacid and a particular semicrystalline polyester prepared bypolyesterification of a saturated aliphatic dicarboxylic acid having alinear chain with a saturated aliphatic diol having a linear orcycloaliphatic chain, such as those described in detail above, arecapable of providing low-gloss or matt coatings having good mechanicalproperties and excellent weatherability. This is because it has beenobserved that powders which have an identical composition but in whichthe amorphous polyester rich in isophthalic acid is replaced by anamorphous polyester rich in terephthalic acid, of the type of thosedescribed and used in U.S. Pat. No. 5,373,084 give, after curing, acoating having a very high gloss (Comparative Example I). Likewise, ithas been observed that powders which have an identical composition butin which the particular semicrystalline polyester according to theinvention is replaced by a semicrystalline polyester that is notaccording to the invention, of the type of those described and used inEuropean Patent 521,992 and essentially based on terephthalic acid and1,6-hexanediol also give, after curing, a coating having a very highgloss (Comparative Examples II and III).

[0056] The amorphous polyesters rich in isophthalic acid and thesemicrystalline polyesters used according to the invention are preparedby the conventional methods of synthesizing polyesters, using an excessof acid with respect to the alcohol so as to obtain a polyestercontaining carboxyl groups having the desired acid number.

[0057] The amorphous polyesters containing carboxyl groups, rich inisophthalic acid, may be prepared by one-stage or two-stage methods ofsynthesis. In the latter case, in the first stage, a polyestercontaining hydroxyl groups is prepared from, on the one hand,isophthalic acid and, optionally, one or more other polycarboxylic acidsother than isophthalic acid (or their functional derivatives) and from,on the other hand, an excess of neopentylglycol and, optionally, one ormore other dihydroxylated and/or polyhydroxylated compounds and, in thesecond stage, the polyester containing hydroxyl groups thus obtained isesterified with an appropriate dicarboxylic acid, preferably isophthalicacid, in order to obtain an amorphous polyester containing carboxylgroups, rich in isophthalic acid.

[0058] The semicrystalline polyesters containing carboxyl groups aregenerally prepared using a one-stage process from an appropriatealiphatic or cycloaliphatic diol and from an excess of the appropriatealiphatic dicarboxylic acid, optionally incorporating a polycarboxylicacid or a polyol into the reaction mixture if it is desired to obtain abranched semicrystalline polyester.

[0059] The synthesis of these polyesters is generally carried out in aconventional reactor fitted with a stirrer, with an influx of inert gas(for example, nitrogen), with a distillation column connected to acondenser and with a thermometer attached to a temperature controller.

[0060] The esterification conditions are conventional, namely that astandard esterification catalyst may be used, either a tin derivative,such as dibutyltin dilaurate, dibutyltin oxide or n-butyltintrioctanoate, or a titanium derivative, such as tetrabutyl titanate, inan amount ranging from 0.01 to 1% by weight of the reactants. To thismay optionally be added an antioxidant of the phenolic type, such asIrganox 1010 (sold by Ciba-Geigy), by itself or in a mixture with astabilizer, such as, for example tributyl phosphite, in an amountranging from 0.01 to 1% by weight of the reactants.

[0061] The polyesterification is generally carried out at a temperaturewhich is gradually increased from approximately 130° C. to approximately180 to 250° C., firstly under normal pressure and then under reducedpressure, maintaining this temperature until the formation of apolyester having the desired hydroxyl number and/or acid number. When atwo-stage process is used to prepare the amorphous polyesters rich inisophthalic acid, the reaction mixture containing the polyestercontaining hydroxyl groups that was obtained in the first stage is leftto cool down to 200° C., the desired amount of dicarboxylic acid isadded, the temperature is raised to 230-240° C. and this temperature ismaintained firstly under normal pressure and then under reducedpressure, until the formation of an amorphous polyester containingcarboxyl groups having the desired acid number.

[0062] The degree of esterification is monitored by determining theamount of water formed during the reaction and the properties of thepolyester obtained, for example the acid number, the hydroxyl number,the molecular weight, the glass transition temperature (T_(g)), themelting point (T_(m)) and the melt viscosity.

[0063] At the end of the synthesis, when the polyester is still in themolten state, a crosslinking catalyst, known per se, may optionally beadded to it in an amount ranging from 0.01 to 1.5% by weight of thepolyester. These catalysts may be of the amine type, such as2-phenylimidazoline, of the phosphine type, such as triphenylphosphine,or ammonium or phosphonium salts, such as tetrapropylammonium chloride,tetrabutylammonium bromide, benzyltriphenylphosphonium chloride orethyltriphenylphosphonium bromide. Next, the polyester is removed fromthe reactor and cast as a thick layer, left to cool and ground intoparticles having an average size ranging from a fraction of an mm toseveral mm.

[0064] The amorphous polyester containing carboxyl groups, rich inisophthalic acid, the semicrystalline polyester containing carboxylgroups and the crosslinking agent together form the basic binder for thethermosetting powder coating compositions according to the invention.

[0065] In the thermosetting powder coating compositions according to theinvention, the amount of amorphous polyester rich in isophthalic acidgenerally represents approximately 60 to 87% by weight and the amount ofsemicrystalline polyester approximately 13 to 40% by weight calculatedwith respect to the total weight of the amorphous polyester and of thesemicrystalline polyester. However, it has been observed that the gloss,measured at an angle of 60° C. according to the ASTM D 523 standard, ofthe coatings obtained decreases when the amount of amorphous polyesterdecreases and the amount of semicrystalline polyester increases. This iswhy, in the compositions according to the invention, the amount ofamorphous polyester rich in isophthalic acid preferably represents 60 to82% by weight and the amount of semicrystalline polyester preferablyrepresents 18 to 40% by weight calculated with respect to the totalweight of the amorphous polyester and of the semicrystalline polyester.

[0066] The crosslinking agents which may be used in the compositionsaccording to the invention are all organic compounds having functionalgroups capable of reacting with the carboxyl groups of the polyesters inorder to crosslink the binder. Typical crosslinking agents are, forexample, polyepoxidized compounds and β-hydroxyalkylamides. Particularlypreferred crosslinking agents are triglycidyl isocyanurate (ARALDITE PT810 sold by Ciba-Geigy), the 75/25 mixture of diglycidyl terephthalateand of triglycidyl trimellitate (ARALDITE PT 910 sold by Ciba-Geigy),acrylic copolymers containing glycidyl groups, such as GMA 252 sold byEstron, and bis(N,N-dihydroxyethyl)-adipamide (PRIMID XL 552 sold byEMS).

[0067] In the thermosetting powder coating compositions according to theinvention, the ratio of the amount of amorphous polyester and ofsemicrystalline polyester containing carboxyl groups, on the one hand,to the amount of crosslinking agent, on the other hand, is such thatthere are from 0.5 to 1.5 equivalents of carboxyl groups per equivalentof functional groups (for example, epoxy groups) in the crosslinkingagent.

[0068] It is preferred to use the crosslinking agent in an amount ofapproximately 4 to 25% by weight calculated with respect to the totalweight of the binder.

[0069] The powder coating compositions according to the inventiontherefore generally contain, as binder,

[0070] (a) from 45 to 83% by weight of amorphous polyester rich inisophthalic acid, (b) from 13 to 30% by weight of semicrystallinepolyester and (c) from 4 to 25% by weight of crosslinking agent, andpreferably (a) from 45 to 78% by weight of amorphous polyester rich inisophthalic acid, (b) from 18 to 30% by weight of semicrystallinepolyester and (c) from 4 to 25% by weight of crosslinking agent.

[0071] The present invention also relates to the use of thethermosetting powder coating compositions according to the invention forthe preparation of powder paints and varnishes that provide low-glosscoatings, preferably matt coatings, as well as to the powder paints andvarnishes obtained using these compositions.

[0072] The powder paints and varnishes according to the invention may beprepared by mixing in a homogeneous manner the amorphous polyester richin isophthalic acid, the semicrystalline polyester and the crosslinkingagent with the various auxiliary substances conventionally used for themanufacture of powder paints and varnishes.

[0073] This homogenization is carried out, for example, by firstly dryblending, at ambient temperature, the amorphous polyester, thesemicrystalline polyester, the crosslinking agent and the variousauxiliary substances in a mixer, for example a drum mixer, and by thenpassing the blend thus obtained through an extruder, for example asingle-screw extruder of the Buss-Ko-Kneter type or a twin-screwextruder of the PRISM or A.P.V. type in order to produce melthomogenization therein at a temperature lying within the range 80 to150° C. The extrudate is then left to cool, ground and screened in orderto obtain a powder whose particle size is between 10 and 150micrometres.

[0074] If desired, the amorphous polyester rich in isophthalic acid andthe semicrystalline polyester may be melt blended beforehand in thesynthesis reactor or in an extruder, such as a Betol BTS 40 extruder,before they are added in the form of a blend to the other ingredients ofthe composition for the dry blending at ambient temperature. However, itis more convenient to add the two polyesters separately to the otheringredients of the powder composition.

[0075] The auxiliary substances which may be added to the thermosettingpowder coating compositions are, for example, pigments and colorants,such as titanium dioxide, iron oxides, zinc oxide, etc., metalhydroxides, metal powders, sulphides, sulphates, carbonates, silicates,such as ammonium silicate for example, carbon black, talc, kaolins,barytes, iron blues, lead blues, organic reds, organic browns, etc.,flow-regulating agents, such as RESIFLOW PV5 (from Worlee), MODAFLOW(from Monsanto) or ACRONAL 4F (from BASF), and air-release agents, suchas benzoin, etc. These auxiliary substances are used in the usualamounts, it being understood that if the thermosetting compositionsaccording to the invention are used as varnishes the addition ofopacifying substances will be omitted. It is also possible to addcompounds that absorb ultraviolet radiation, such as TINUVIN 900 fromCiba-Geigy and sterically hindered amine-based light stabilizers, suchas TINUVIN 144 from Ciba-Geigy.

[0076] The subject of the present invention is also a process forobtaining a low-gloss coating on an article, in which process athermosetting powder coating composition according to the invention, asdescribed above, is applied to the said article and the article thuscoated is cured at a high temperature for a time long enough tocompletely crosslink the coating.

[0077] The thermosetting powder coating compositions may be applied toarticles of various shapes and sizes, in particular to articles made ofglass, of ceramic and of metal, such as steel and aluminium, usingtechniques known per se for depositing powders, that is to say by usinga spray gun in an electrostatic field in which the powder is chargedunder a voltage of 30 to 100 kV by a high-voltage direct current, or byusing a triboelectric spray gun in which the powder is charged byfriction, or else by the well-known technique of fluidized-beddeposition.

[0078] After they have been applied to the article in question, thedeposited powders are oven-cured at a temperature of between 140 and200° C. for a time which may be as long as 30 minutes in order to meltthe powder particles, to form a homogeneous skin, which spreadsperfectly over the substrate, and finally to achieve completecrosslinking and curing of the coating.

[0079] The thermosetting powder coating compositions according to thepresent invention allow coatings to be obtained which have a low gloss.This is because the gloss, measured at an angle of 60° C. according tothe ASTM D 523 standard, of these coatings always has a value of lessthan 50%.

[0080] In addition, as has already been explained above, it is possibleto obtain coatings having different levels of gloss depending on theamount of amorphous polyester and on the amount of semicrystallinepolyester that are used in these compositions.

[0081] By virtue of the present invention, it is therefore possible,after curing, to obtain coatings having the desired level of glosssimply by choosing a powder, composition which contains the requiredproportions of amorphous polyester and of semicrystalline polyester.

[0082] However, account should be taken of the fact that the nature ofthe crosslinking agent is also important with respect to the level ofgloss of the coatings obtained after curing (see Example 11 below). Afew preliminary tests will make it possible to easily determine thecomposition that, is suitable for obtaining a coating which has thedesired level of gloss.

[0083] As shown in greater detail in the examples which follow, it istherefore possible, by virtue of the present invention, to preparepowder paints and varnishes capable of providing coatings having thelevel of gloss required by the application envisaged, that is to saysatin or semi-gloss coatings, the gloss of which, measured at an angleof 60° C. according to the ASTM D 523 standard, is less than 50%, ormatt coatings, the gloss of which, measured under the same conditions,is less than 35%.

[0084] Furthermore, the thermosetting powder compositions according tothe present invention are capable of producing low-gloss coatings havinga combination of other advantageous properties, inter alia a smooth anduniform appearance, without any surface defects and free of “orangepeel”, good mechanical properties, and excellent weatherability and UVresistance. The formation of a satin or matt finish is therefore notaccompanied by a deterioration in the other properties of the coatings,as is often the case with powder compositions of the prior art that arecapable of producing low-gloss coatings.

[0085] Finally, another important advantage of the thermosetting powdercoating compositions according to the present invention over the powdercompositions of the prior art resides in the fact that their propertiesare only slightly sensitive, or are insensitive, to variations in theextrusion conditions and that these compositions therefore make itpossible to continually produce low-gloss, satin or matt coatings havingsubstantially the same degree of gloss or of mattness.

[0086] The examples which follow illustrate the invention withoutlimiting it. In these examples, certain characteristic values have beendetermined according to the methods described below:

[0087] gloss: this is expressed as the intensity of the reflected light,in percent, with respect to the intensity of the light incident at anangle of 60° and measured according to the ASTM D 523 standard;

[0088] impact strength: this is measured by means of a Gardner apparatusaccording to the ASTM D 2794 standard. Cold-rolled steel panels providedwith a cured coating are subjected to impacts of increasing intensity onthe coated side (direct impact) and on the uncoated side (reverseimpact). The highest impact that does not cause the coating to crack ismeasured in kg.cm;

[0089] pencil hardness: this is determined by means of a WOLFF WILBRONhardness tester (ASTM D 3363 standard); the hardness measured is that ofthe hardest pencil that does not cause a notch in the coating accordingto a scale which goes from 6B (the softest pencil) to 6H (the hardestpencil);

[0090] QUV accelerated ageing test: chromium-plated aluminium panelsprovided with a cured coating to be tested are placed in a “QUV Panel”test apparatus from the company Q-Panel Co. (Cleveland, USA), andsubjected to several cycles of exposure to UV lamps and to moisture, atvarious temperatures. Among the various cycles of this type that aredescribed in the ASTM G 53-88 standard, the coatings in the present casewere subjected to a cycle of 8 hours' exposure to a fluorescent UVA lamp(340 nm wavelength and 0.77 W/m²/nm intensity) simulating the harmfuleffects of sunlight, at 60° C., and of 4 hours of water vapourcondensation, with the lamp off, at 40° C.; the change in gloss,measured at an angle of 60°, according to the ASTM D 523 standard, isnoted. After 3000 hours' exposure to this test, the gloss retention wasdetermined from the equation:${\% \quad {retention}} = {\frac{60^{{^\circ}}\quad {gloss}\quad {after}\quad 3000\quad {hours}^{\prime}\quad {exposure}}{60^{{^\circ}}\quad {gloss}\quad {at}\quad {the}\quad {start}\quad {of}\quad {the}\quad {experiment}} \times 100\quad \%}$

[0091] and also the colour change delta E, calculated according to theASTM D 2244 standard;

[0092] the acid number and the hydroxyl number were determined bytitration according to the DIN 53402 and DIN 53240 standards andexpressed in mg of KOH per gramme of polyester;

[0093] the glass transition temperature (T_(g)) and the melting point(T_(m)) were determined by differential scanning calorimetry (DSC) at ascan rate of 20° C. per minute;

[0094] the number-average molecular weight ({overscore (M)}_(n)) of thepolyesters was determined from the equation:${\overset{\_}{M}}_{n} = \frac{{functionality} \times 56,100}{N_{A}}$

[0095] where N_(A) is the acid number expressed in mg of KOH per grammeof polyester; and

[0096] the melt viscosity of the polyesters, expressed in mPa.s, wasmeasured by means of an ICI cone-and-plate viscometer according to theASTM D 4287-88 standard; it is also called the “ICI viscosity” and wasmeasured at the temperatures indicated in the examples.

[0097] Unless otherwise indicated, the parts mentioned in the examplesare parts by weight.

EXAMPLE 1 Synthesis of Amorphous Polyesters

[0098] a) One-Stage Synthesis

[0099] A mixture a 399.6 parts (3.84 mol) of neopentylglycol and 22.2parts (0.16 mol) of trimethylolpropane is introduced into a 10 litrefour-necked round-bottomed flask provided with a stirrer, a nitrogeninflux and a distillation column connected to a water-cooled condenserand a thermometer attached to a temperature controller. The mixture isheated, with stirring and under nitrogen, to a temperature ofapproximately 130° C. and added to it are 722.9 parts (4.35 mol) ofisophthalic acid and 2.5 parts of n-butyltin trioctanoate asesterification catalyst. The temperature of the reaction mixture is thengradually raised to 230° C. Water starts to distil from the reactorabove 180° C. When the distillation of water at atmospheric pressure iscompleted, a vacuum of 50 mm Hg is gradually created. The temperature ofthe reaction mixture is maintained for 3 hours at 230° C. and at apressure of 50 mm Hg.

[0100] Finally, the polyester obtained is left to cool to 180° C. andremoved from the reactor.

[0101] The polyester containing carboxyl groups thus obtained has thefollowing characteristics: Acid number 32 mg of KOH/g Hydroxyl number  2mg of KOH/g ICI viscosity (at 200° C.) 8000 mPa · s Glass transitiontempera- ture (T_(g)) 59° C. (DSC at 20° C./minute) Number-averagemolecular 5423 (theoretical) weight ({overscore (M)}n)

[0102] b) Two-Stage Synthesis

[0103] 1st Stage:

[0104] A mixture of 423.5 parts (4.07 mol) of neopentylglycol and 22.2parts (0.16 mol) of trimethylolpropane is introduced into a reactor asdescribed at a) above. The mixture is heated with stirring and undernitrogen to a temperature of approximately 130° C. and added to it are121.8 parts (0.733 mol) of terephthalic acid, 487.1 parts (2.93 mol) ofisophthalic acid and 2.3 parts of n-butyltin trioctanoate asesterification catalyst.

[0105] The reaction is continued at 220° C. and under atmosphericpressure until approximately 95% of the theoretical amount of water isdistilled. A transparent polyester containing hydroxyl groups isobtained which has the following characteristics: Hydroxyl number 59 mgof KOH/g Acid number 12 mg of KOH/g ICI viscosity (at 175° C.) 2200 mPa· s

[0106] 2nd Stage:

[0107] The polyester obtained at the first stage is left too cool to200° C. and added to it are 110.9 parts (0.67 mol) of isophthalic acid.Next, the mixture is gradually heated to 230° C. The mixture ismaintained at this temperature for 2 hours and, when the reactionmixture becomes clear, a vacuum of 50 mm Hg is gradually created. Thereaction is continued for 3 hours at 230° C. and under a pressure of 50mm Hg.

[0108] The polyester containing carboxyl groups thus obtained has thefollowing properties: Acid number 31 mg of KOH/g Hydroxyl number  3 mgof KOH/g ICI viscosity (at 200° C.) 6600 mPa · s Glass transitiontempera- 57° C. ture (T_(g)) (DSC at 20W/minute) Number-averagemolecular 5423 (theoretical) weight ({overscore (M)}n)

[0109] c) Yet another amorphous polyester containing carboxyl groups,rich in isophthalic acid, is prepared using the two-stage operatingmethod described in b) above.

[0110] In the first stage, a polyester containing hydroxyl groups isprepared in the same way as in b) above from 423.5 parts (4.07 mol) ofneopentylglycol, 304.5 parts (1.83 mol) of terephthalic acid, 304.5parts (1.83 mol) of isophthalic acid and 2.3 parts of n-butyltintrioctanoate as esterification catalyst. The reaction is carried outunder atmospheric pressure at 230° C. (instead of 220° C.).

[0111] The transparent polyester containing hydroxyl groups has thefollowing characteristics: Hydroxyl number 57 mg of KOH/g Acid number 13mg of KOH/g ICI viscosity (at 175° C.) 1200 mPa · s

[0112] In the second stage, a polyester containing carboxyl groups isprepared in the same way as in b) above: 110.9 parts (0.67 mol) ofisophthalic acid are added as in b) above.

[0113] The polyester containing carboxyl groups thus obtained has thefollowing characteristics: Acid number  32 mg of KOH/g Hydroxyl number2.1 mg of KOH/g ICI viscosity (at 200° C.) 3000 mPa · s Glass transitiontempera- 53° C. ture (T_(g)) (DSC at 20° C./minute) Number-averagemolecular 3740 (theoretical) weight ({overscore (M)}n)

[0114] d) By way of comparison, an amorphous polyester containingcarboxyl groups, rich in terephthalic acid, is also prepared accordingto the two-stage operating method described in b) above; it contains aminor amount of isophthalic acid (16.2 mol %) and a major amount ofterephthalic acid (83.8 mol %).

[0115] In the first stage, a polyester containing hydroxyl groups isprepared in the same manner as in b) above from 417.8 parts (4.02 mol)of neopentylglycol, 600.7 parts (3.62 mol) of terephthalic acid and 2.2parts of n-butyltin trioctanoate as esterification catalyst. Thereaction is carried out under atmospheric pressure at 240° C. (insteadof 220° C.).

[0116] The transparent polyester containing hydroxyl groups has thefollowing characteristics: Hydroxyl number 61 mg of KOH/g Acid number  8mg of KOH/g ICI viscosity (at 200° C.) 1200 mPa · s

[0117] In the second stage, a polyester containing carboxyl groups isprepared in the same way as in b) above, but 117.1 parts (0.7 mol) ofisophthalic acid are added (instead of 110.9 parts); the mixture isgradually heated to 240° C. (instead of 230° C.) and it is maintained atthis temperature for 3 hours. When the reaction mixture becomes clear, avacuum of 50 mm of Hg is gradually created and the reaction continuedfor 4 hours at 240° C. and under a pressure of 50 mm Hg.

[0118] The polyester containing carboxyl groups thus obtained has thefollowing characteristics: Acid number 33 mg of KOH/g Hydroxyl number  3mg of KOH/g ICI viscosity (at 200° C.) 4700 mPa · s Glass transitiontempera- 57° C. ture (T_(g)) (DSC at 20° C./minute) Number-averagemolecular 3740 (theoretical) weight ({overscore (M)}n)

[0119] The polyester obtained is left to cool to 200° C. and added to itare 1.3 parts of ethyltriphenylphosphonium bromide (crosslinkingcatalyst). After stirring the mixture for one hour, the polyester isremoved from the reactor.

[0120] e) Another amorphous polyester containing carboxyl groups, richin isophthalic acid, is prepared using the one-stage operating methoddescribed in a) above from 424.9 parts of neopentylglycol, 722.2 partsof isophthalic acid and 2.3 parts of n-butyltin trioctanoate asesterification catalyst. The polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 31.5 mg of KOH/gICI viscosity (at 200° C.) 2900 mPa · s Glass transition tempera- 52° C.Lure (T_(g)) (DSC at 20° C./minute)

EXAMPLE 2 Synthesis of Semicrystalline Polyesters

[0121] a) A mixture of 739.9 parts (3.21 mol) of 1,12-dodecanedioicacid, 369.2 parts (3.12 mol) of 1,6-hexanediol and 2.5 parts ofn-butyltin trioctanoate as esterification catalyst are introduced into areactor as described in Example 1.

[0122] The mixture is heated, with stirring and under nitrogen, to atemperature of approximately 140° C., at which temperature the waterstarts to distil from the reactor. The temperature of the reactionmixture is then gradually raised to 225° C. When the distillation ofwater at atmospheric pressure is completed, 1.0 part of tributylphosphite as stabilizer and 1.0 part of n-butyltin trioctanoate areadded and a vacuum of 50 mm Hg is gradually created. The temperature ofthe reaction mixture is maintained for 3 hours at 225° C. and under apressure of 50 mm Hg.

[0123] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 11.5 mg of KOH/gHydroxyl number  0.5 mg of KOH/g ICI viscosity (at 150° C.) 7000 mPa · sMelting point (T_(m)) 67° C. (DSC at 20° C./minute) Number-averagemolecular 11220 (theoretical) weight ({overscore (M)}n)

[0124] The polyester obtained is left to cool to 160° C. and added to itare 10 parts of TINUVIN 144 (light stabilizer) and 20 parts of TINUVIN900 (UV light absorber). After stirring the mixture for one hour, thepolyester is removed from the reactor, left to cool to ambienttemperature and obtained in the form of a white solid substance.

[0125] b) Another semicrystalline polyester is prepared using theoperating method described in a) above from 750.7 parts (3.26 mol) of1,12-dodecanedioic acid, 353.7 parts (2.99 mol) of 1,6-hexanediol and2.5 parts of n-butyltin trioctanoate as esterification catalyst.

[0126] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 29.5 mg of KOH/gHydroxyl number  0.6 mg of KOH/g ICI viscosity (at 100° C.) 2000 mPa · sMelting point (T_(m)) 65° C. (DSC at 20° C./minute) Number-averagemolecular 3740 (theoretical) weight ({overscore (M)}n)

[0127] The polyester obtained is left to cool to 160° C. and added to itare 10 parts of TINUVIN 144 and 20 parts of TINUVIN 900. After stirringthe mixture for one hour, the polyester is removed from the reactor,left to cool to ambient temperature and obtained in the form of a whitesolid substance.

[0128] c) Another semicrystalline polyester is prepared using theoperating method described in a) above from 750.2 parts (3.25 mol) of1,12-dodecanedioic acid, 351.2 parts (2.97 mol) of 1,6-hexanediol, 9.567parts (0.07 mol) of trimethylolpropane and 2.5 parts of n-butyltintrioctanoate as esterification catalyst.

[0129] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 21.3 mg of KOH/gHydroxyl number 0.9 mg of KOH/g ICI viscosity (at 100° C.) 4000 mPa.sMelting point (T_(m)) 63° C. (DSC at 20° C./minute) Number-averagemolecular 7012 (theoretical) weight ({overscore (M)}_(n))

[0130] The polyester obtained is left to cool to 160° C. and added to itare 10 parts of TINUVIN 144 and 20 parts of TINUVIN 900. After stirringthe mixture for one hour, the polyester is removed from the reactor,left to cool to ambient temperature and obtained in the form of a whitesolid substance.

[0131] d) Another semicrystalline polyester is prepared using theoperating method described in a) above from 897.4 parts (3.90 mol) of1,12-dodecanedioic acid, 236.4 parts (3.81 mol) of ethylene glycol and2.5 parts of n-butyltin trioctanoate as esterification catalyst.

[0132] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 8.0 mg of KOH/gHydroxyl number 2.5 mg of KOH/g ICI viscosity (at 150° C.) 7200 mPa.sMelting point (T_(m)) 76° C. (DSC at 20° C./minute) Number-averagemolecular 11220 (theoretical) weight ({overscore (M)}_(n))

[0133] The polyester obtained is left to cool to 160° C. and added to itare 10 parts of TINUVIN 144 and 20 parts of TINUVIN 900. After stirringthe mixture for one hour, the polyester is removed from the reactor,left to cool to ambient temperature and obtained in the form of a whitesolid substance.

[0134] e) By way of comparison, a semicrystalline polyester containingcarboxyl groups not according to the invention is also prepared in thefollowing manner:

[0135] 1st Stage:

[0136] 453.4 parts (3.84 mol) of 1,6-hexanediol are introduced into areactor as described in Example 1. The contents of the reactor areheated up to 150° C. in order to melt the substance and added to it are589.9 parts (3.55 mol) of terephthalic acid and 2.3 parts of n-butyltintrioctanoate as esterification catalyst. The reaction is continued at235° C. under atmospheric pressure until approximately 95% of thetheoretical amount of water is distilled. A polyester containinghydroxyl groups is obtained which has the following characteristics:Hydroxyl number 40 mg of KOH/g Acid number 5 mg of KOH/g ICI viscosity(at 175° C.) 800 mPa.s

[0137] 2nd Stage:

[0138] The polyester obtained in the first stage is left to cool to 200°C. and added to it are 91.7 parts (0.55 mol) of isophthalic acid. Next,the mixture is gradually heated to 235° C. The mixture is maintained atthis temperature for 2 hours, 1.0 part of tributylphosphite is added asstabilizer and a vacuum of 50 mm Hg is gradually created. Thetemperature of the reaction mixture is maintained for 2 hours at 235° C.under a pressure of 50 mm Hg. The semicrystalline polyester containingcarboxyl groups thus obtained has the following characteristics: Acidnumber 32 mg of KOH/g Hydroxyl number 0.5 mg of KOH/g ICI viscosity (at150° C.) 7200 mPa.s Melting point (T_(m)) 130° C. (DSC at 20° C./minute)Number-average molecular 3740 (theoretical) weight ({overscore (M)}_(n))

[0139] The polyester obtained is left to cool to 160° C. and added to itare 10 parts of TINUVIN 144 and 20 parts of TINUVIN 900. After stirringthe mixture for one hour, the polyester is removed from the reactor,left to cool to ambient temperature and obtained in the form of a whitesolid substance.

[0140] f) By way of comparison, yet another semicrystalline polyester isprepared in exactly the same way as in d) above from 458.24 parts (3.88mol) of 1,6-hexanediol and 589.2 parts (3.55 mol) of terephthalic acid(in the first stage) and from 91.4 parts (0.62 mol) of adipic acid (inthe second stage).

[0141] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 34 mg of KOH/gHydroxyl number  / 3 mg of KOH/g ICI viscosity (at 200° C.) 700 mPa.sMelting point (T_(m)) 129° C. (DSC at 20° C./minute) Number-averagemolecular 3400 (theoretical) weight ({overscore (M)}_(n))

[0142] This semicrystalline polyester has the same characteristics asthe semicrystalline polyester described in Example 1a of European Patent521,992.

[0143] On completion of the synthesis, the polyester obtained is left tocool and added to it are 10 parts of TINUVIN 144 and 20 parts of TINUVIN900. After stirring the mixture for one hour, the polyester is removedfrom the reactor, left to cool to ambient temperature and obtained inthe form of a white solid substance.

[0144] g) Another semicrystalline polyester is prepared using theoperating method described in a) above from 757.8 parts of1,12-dodecanedioic acid, 351.2 parts of 1,4-cyclohexanediol And 2.5parts of n-butyltin trioctanoate as esterification catalyst. Thesemicrystalline polyester containing carboxyl groups thus obtained hasthe following characteristics: Acid number 31.3 mg of KOH/g ICIviscosity (at 150° C.) 1500 mPa.s Melting point (T_(m)) 65° C. (DSC at20° C./minute)

[0145] h) Another semicrystalline polyester is prepared using theoperating method described in a) above from 700.1 parts of1,12-dodecanedioic acid, 399.8 parts of 1,4-cyclohexanedimethanol and2.5 parts of n-butyltin trioctanoate as esterification catalyst.

[0146] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 33.4 mg of KOH/gICI viscosity (at 150° C.) 1500 mPa.s Melting point (T_(m)) 47° C. (DSCat 20° C./minute)

[0147] i) Another semicrystalline polyester is prepared using theoperating method described in a) above from 709.4 parts of1,12-dodecanedioic acid, 369.74 parts of 1,4-cyclohexanedimethanol and2.5 parts of n-butyltin trioctanoate as esterification catalyst.

[0148] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 33.0 mg of KOH/gICI viscosity (at 150° C.) 3400 mPa.s Melting point (T_(m)) 45° C. (DSCat 20° C./minute)

[0149] j) Another semicrystalline polyester is prepared using theoperating method described in a) above from 500.7 parts of1,12-dodecanedioic acid, 166.9 parts of adipic acid, 439.8 parts of1,4-cyclohexanedimethanol and 2.5 parts of n-butyltin trioctanoate asesterification catalyst.

[0150] The semicrystalline polyester containing carboxyl groups thusobtained has the following characteristics: Acid number 32.4 mg of KOH/gICI viscosity (at 150° C.) 1300 mPa.s Melting point (T_(m)) 45° C. (DSCat 20° C./minute)

EXAMPLES 3 TO 15 AND COMPARATIVE EXAMPLES I, II AND III

[0151] Preparation of Thermosetting Powder Coating Compositions.

[0152] Sixteen thermosetting powder compositions are prepared in thefollowing manner. An amorphous polyester containing carboxyl groups,prepared as described in Example 1, a semicrystalline polyestercontaining carboxyl groups, prepared as described in Example 2, acrosslinking agent and various auxiliary substances conventionally usedfor the manufacture of powder paints are dry blended at ambienttemperature. The nature and the amounts of these substances are given inTable I below. The blend obtained is homogenized in a twin-screwextruder (PRISM, 16 mm, 15/1 L/D) at an extrusion temperature of 85° C.The extrudate is cooled, crushed and ground in a RETSCH ZM 100 mill (0.5μm screen) and then screened in order to form a powder whose particlesize is between 10 and 100 micrometres.

[0153] In order to determine the properties of the coatings obtainedusing these compositions, the powders obtained are deposited by sprayingthem with a Gema-Volstatic PCG 1 electrostatic spray gun on tocold-rolled steel panels under a voltage of 60 to 100 kV so as to obtaina film thickness of between 50 and 70 micrometres.

[0154] The panels thus coated are then transferred into anair-ventilated oven, where the compositions deposited are cured for 15minutes at a temperature of 200° C.

[0155] The cured coatings obtained all have a smooth and uniformappearance and have no defects such as craters, pinholes or “orangepeel”.

[0156] The various compositions and the properties of the coatingsobtained are described in Table I below. TABLE I Examples of whitepaints Composition (parts by weight) 3 4 5 6 7 8 9 10 11 12 13 14 15 I(1) II (1) III (1) Amorphous polyester of Example 1a 423 446.4 441.6 — —441.6 446.4 474.3 427.3 — — — 512.9 — 446.4 446.4 of Example 1b — — —446.4 — — — — — — — — — — — — of Example 1c — — — — 423 — — — — — — — —— — — of Example 1d⁽¹⁾ — — — — — — — — — — — — — 446.4 — — of Example 1e— — — — — — — — — 512.9 512.9 512.9 — — — — Semicrystalline polyester ofExample 2a 141 111.6 110.4 111.6 141 — — — 142.5 — — — — 111.6 — — ofExample 2b — — — — — — — 83.7 — — — — — — — — of Example 2c — — — — —110.4 — — — — — — — — — — of Example 2d — — — — — — 111.6 — — — — — — —— — of Example 2e⁽¹⁾ — — — — — — — — — — — — — — 111.6 — of Example2f⁽¹⁾⁽⁷⁾ — — — — — — — — — — — — — — — 111.6 of Example 2g — — — — — — —— — 128.5 — — — — — — of Example 2h — — — — — — — — — — 128.5 — — — — —of Example 2i — — — — — — — — — — — 128.5 — — — — of Example 2j — — — —— — — — — — — — 128.5 — — — Crosslinking 36 42 — 42 36 — 42 42 — 48.348.3 48.3 48.3 42 42 42 agent A⁽²⁾ Crosslinking — — 48 — — 48 — — — — —— — — — — agent B⁽³⁾ Crosslinking — — — — — — — — 30 — — — — — — — agentC⁽⁴⁾ Titanium dioxide⁽⁵⁾ 300 300 300 300 300 300 300 300 300 296 296 296296 300 300 300 Fix F white 100 100 100 100 100 100 100 100 100 — — — —100 100 100 Flow-regulating 10 10 10 10 10 10 10 10 10 9.9 9.9 9.9 9.910 10 10 agent⁽⁶⁾ Benzoin 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.4 3.43.4 3.4 3.5 3.5 3.5 BTC⁽⁸⁾ — — — — — — — — — 1.0 1.0 1.0 1.0 — — —Properties 60° gloss 18 29 23 25 34 29 28 44 49 40 35 49 48 81 84 86Impact strength (kg · cm) direct 200 200 80 140 180 100 160 120 200 100100 200 140 160 40 60 reverse 200 200 100 160 180 120 160 120 200 100 80200 140 160 20 40 Pencil hardness H 2H H H H H H 2H H — — — — H H 2H

[0157] It may be seen that only the compositions according to theinvention containing both an amorphous polyester rich in isophthalicacid and a semicrystalline polyester prepared from a saturated aliphaticdicarboxylic acid with a linear chain (1,12-dodecanedioic acid) and froma saturated aliphatic diol with a linear chain (1,6-hexanediol orethylene glycol) or from a cycloaliphatic diol (1,4-cyclohexanediol or1,4-cyclohexanedimethanol) give coatings whose gloss is less than 50%.

[0158] The composition of Comparative Example I, which contains anamorphous polyester rich in terephthalic acid, gives a coating which isvery glossy (gloss of 81%).

[0159] Likewise, the compositions of Comparative Example II and ofExample III which contain a semicrystalline polyester not according tothe invention, essentially based on terephthalic acid and 1,6-hexanediol(as in the illustrative embodiments in European Patent 521,992), givecoatings which are very glossy (gloss of 84-86%). Furthermore, thecoatings obtained from these compositions have an impact strength and aflexibility which are inferior.

[0160] It may also be seen that, when a polyepoxidized compound is usedin the composition as crosslinking agent and when the amount ofsemicrystalline polyester increases (from 15 to 25% by weight) and theamount of amorphous polyester decreases (from 85 to 75% by weight withrespect to the total weight of the polyesters), the gloss goes from 44to 18% (compare Examples 10 and 3).

[0161] A coating may therefore be produced which has the desired levelof gloss, either a matt coating (Examples 3 to 9) or a satin orsemi-gloss coating (Examples 10 and 11), just by appositely choosing thepowder composition which provides this level of gloss.

EXAMPLES 16 AND 17 AND COMPARATIVE EXAMPLES IV TO VI

[0162] Preparation of Thermosetting Powder Coating Compositions.

[0163] In these examples and comparative examples, 5 thermosettingpowder compositions are prepared using the operating method described inthe above Examples 3 to 15 for the purpose of obtaining dark brownpaints and of testing the properties of the coatings obtained.

[0164] The various compositions and the properties of the coatingsobtained are given in Table II below.

[0165] The cured coatings obtained from these compositions all have asmooth and uniform appearance and have no defects. TABLE II Examples ofdark brown paints Composition (parts by weight) 16 17 IV (1) V (1) VI(1) Amorphous polyester of Example 1a — 635.6 — 635.6 747.7 of Example1b 598.2 — 598.2 — — Semicrystalline polyester of Example 2a — 112.2 — —— of Example 2b 149.5 — — — — of Example 2e⁽¹⁾ — — 149.5 112.2 —Crosslinking agent A⁽²⁾ 56.3 56.3 56.3 56.3 56.3 Black iron oxide⁽³⁾ 4545 45 45 45 Black iron oxide⁽⁴⁾ 140 140 140 140 140 Carbon black⁽⁵⁾ 1111 11 11 11 Flow-regulating agent⁽⁶⁾ 10 10 10 10 10 Benzoin 3.5 3.5 3.53.5 3.5 Properties 60° gloss 32 44 85 90 87 Impact resistance (kg · cm)direct 100 180 120 60 0 reverse 100 200 120 40 0 Pencil hardness H 2H H2H 2H

[0166] Table II shows that the compositions according to the invention(Examples 16 and 17) give low-gloss coatings while the compositions notaccording to the invention (Comparative Examples IV and V), whichcontain a semicrystalline polyester essentially based on terephthalicacid and 1,6-hexanediol, give very glossy coatings (gloss of 85 to 90%).

EXAMPLE 18 Weatherability of the Coatings

[0167] In this example, the excellent weather behaviour of the low-glosscoatings obtained from compositions according to the invention isdemonstrated.

[0168] For this purpose, the coatings obtained with the dark brownpaints prepared in Examples 16 and 17 and Comparative Examples IV, V andVI (the compositions of which are given in Table II) were tested withrespect to their weatherability.

[0169] The powder paints to be tested are deposited by spraying themusing a Gema-Volstatic PCG 1 electrostatic spray gun ontochromium-plated aluminium panels under a voltage of 60 to 100 kV. Thethickness of the coating deposited is from 50 to 70 micrometers.

[0170] After curing for 15 minutes at 200° C., the coatings obtained aresubjected to the accelerated ageing test (the QUV test described above)so as to determine the UV resistance and moisture resistance. The colourchange delta E was determined according to the ASTM D 2244 standard andthe retention of the gloss, measured at an angle of 60° C., wasdetermined according to the ASTM D 523 standard after 3000 hoursexposure.

[0171] The results thus obtained are given in Table III in which: firstcolumn indicates the composition tested second column the colour changedelta E calculated according to the ASTM D 2244 standard after 3000hours' exposure third column the retention of the gloss, measured at anangle of 60° C., according to the ASTM D 523 standard after 3000 hours'exposure and expressed as a percentage of its initial value at the startof the experiment.

[0172] TABLE III Accelerated ageing of the coatings Composition Delta ERetention of the gloss (%) of Example 16 5.3 63 of Example 17 3.5 82 ofExample IV⁽¹⁾ 16.8 32 of Example V⁽¹⁾ 15.1 41 of Example VI⁽¹⁾ 4.8 92

[0173] (1) by Way of Comparison.

[0174] The results in Table III show that the low-gloss coatingsobtained from the compositions according to the invention exhibitremarkably good weatherability (Examples 16 and 17).

[0175] This weatherability is comparable to that obtained withcompositions based on amorphous polyesters rich in isophthalic acid thatare commercially available and reknowned for their excellent outdoorexposure performance (Comparative Example VI). The presence of thesemicrystalline polyester based on 1,12-dodecanedioic acid and1,6-hexanediol in the compositions according to the invention hardlyaffects the weatherability of the cured coatings obtained.

[0176] It may be seen in Table III that the same does not apply withregard to the compositions of the prior art which contain asemicrystalline polyester of the type of those used in the illustrativeembodiments of European Patent 521,992, which are based essentially onterephthalic acid and 1,6-hexanediol. This is because the coatingsobtained with these compositions are extensively damaged by exposingthem to UV lamps and to moisture: the colour change delta E is verysignificant and the gloss falls below 50% of its initial value after3000 hours' exposure (comparative Examples IV and V).

1. Thermosetting powder coating compositions comprising, as binder, ablend of an amorphous polyester, of a semicrystalline polyester and of acrosslinking agent, characterized in that the binder comprises: (a) anamorphous polyester containing carboxyl groups, rich in isophthalicacid, prepared from an acid constituent comprising from 55 to 100 mol %of isophthalic acid, from 0 to 45 mol % of at least one dicarboxylicacid other than isophthalic acid and from 0 to 10 mol % of apolycarboxylic acid containing at least 3 carboxyl groups and from analcohol constituent comprising from 60 to 100 mol % of neopentylglycol,from 0 to 40 mol % of at least one dihydroxylated compound other thanneopentylglycol and from 0 to 10 mol % of a polyhydroxylated compoundcontaining at least 3 hydroxyl groups, the said amorphous polyesterhaving a glass transition temperature (T_(g)) of at least 50° C. and anacid number of 15 to 100 mg of KOH/g; (b) a semicrystalline polyestercontaining carboxyl groups prepared either (b1) from a saturatedaliphatic dicarboxylic acid with a linear chain having from 4 to 16carbon atoms and from a saturated aliphatic diol with a linear chainhaving from 2 to 16 carbon atoms and optionally from a polycarboxylicacid containing at least 3 carboxyl groups or from a polyol containingat least 3 hydroxyl groups, or (b2) from 40 to 100 mol % of a saturatedaliphatic dicarboxylic acid with a linear chain having from 10 to 16carbon atoms and from 0 to 60 mol % of an aliphatic dicarboxylic acidwith a linear chain having from 4 to 9 carbon atoms, calculated withrespect to the total of the dicarboxylic acids, from a cycloaliphaticdiol having from 3 to 16 carbon atoms and optionally from apolycarboxylic acid having at least 3 carboxyl groups or from a polyolhaving at least 3 hydroxyl groups, the said semicrystalline polyestershaving a melting point (T_(m)) of at least 40° C. and an acid number of5 to 50 mg of KOH/g; and (c) a crosslinking agent.
 2. Compositionsaccording to claim 1, characterized in that the amorphous polyester (a)has a glass transition temperature of 50 to 80° C. and an acid number of30 to 70 mg of KOH per gramme.
 3. Compositions according to either ofclaims 1 and 2, characterized in that the amorphous polyester (a) has atleast one of the following characteristics: a number-average molecularweight of between 1100 and 11,500 and a melt viscosity of 100 to 15,000mPa.s at 200° C.
 4. Compositions according to any one of claims 1 to 3,characterized in that the acid constituent of the amorphous polyester(a) contains, apart from isophthalic acid, up to 45 mol % of adicarboxylic acid chosen from terephthalic acid, phthalic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, sebacic acid, fumaric acid, maleic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid andmixtures of these compounds.
 5. Compositions according to any one ofclaims 1 to 4, characterized in that the alcohol constituent of theamorphous polyester (a) contains, apart from neopentylglycol, up to 40mol % of a dihydroxylated compound chosen from ethylene glycol,propylene glycol, 1,4-butanediol, 1,6-hexanediol,2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol,1,4-cyclohexanedimethanol, hydrogenated bisphenol A, neopentylglycolhydroxypivalate and mixtures of these compounds.
 6. Compositionsaccording to any one of claims 1 to 5, characterized in that thesemicrystalline polyester (b) has a melting point of between 40 and 90°C., an acid number of 5 to 30 mg of KOH per gramme and a hydroxyl numberwhich does not exceed 5 mg of KOH per gramme.
 7. Compositions accordingto any one of claims 1 to 6, characterized in that the semicrystallinepolyester (b) has at least one of the following characteristics: anumber-average molecular weight of between 2200 and 25,000 and a meltviscosity of from 50 mPa.s at 100° C. to 10,000 mPa.s at 150° C. 8.Compositions according to any one of claims 1 to 7, characterized inthat the semicrystalline polyester (b1) is the polyesterificationproduct of 1,12-dodecanedioic acid with 1,6-hexanediol.
 9. Compositionsaccording to any one of claims 1 to 7, characterized in that thesemicrystalline polyester (b2) is the polyesterification product of1,12-dodecanedioic acid with 1,4-cyclohexanediol or1,4-cyclohexanedimethanol.
 10. Compositions according to any one ofclaims 1 to 9, characterized in that the amount of amorphous polyester(a) represents approximately 60 to 87% by weight and the amount ofsemicrystalline polyester (b) represents approximately 13 to 40% byweight calculated with respect to the total weight of the amorphouspolyester (a) and of the semicrystalline polyester (b).
 11. Compositionsaccording to any one of claims 1 to 9, characterized in that the amountof amorphous polyester represents 60 to 82% by weight and the amount ofsemicrystalline polyester (b) represents 18 to 40% by weight calculatedwith respect to the total weight of the amorphous polyester (a) and ofthe semicrystalline polyester (b).
 12. Compositions according to any oneof claims 1 to 11, characterized in that the crosslinking agent (c) is apolyepoxidized compound.
 13. Compositions according to any one of claims1 to 11, characterized in that the crosslinking agent (c) is abeta-hydroxyalkylamide.
 14. Compositions according to any one of claims1 to 13, characterized in that the ratio of the amount of amorphouspolyester (a) and of semicrystalline polyester (b) containing carboxylgroups, on the one hand, to the amount of crosslinking agent (c), on theother hand, is such that there are from 0.5 to 1.5 equivalents ofcarboxyl groups per equivalent of functional groups in the crosslinkingagent.
 15. Compositions according to any one of claims 1 to 14,characterized in that the crosslinking agent (c) is present in an amountof approximately 4 to 25% by weight calculated with respect to the totalweight of the binder.
 16. Compositions according to any one of claims 1to 15, characterized in that the binder comprises from 45 to 83% byweight of amorphous polyester (a), from 13 to 30% by weight ofsemicrystalline polyester (b) and from 4 to 25% by weight ofcrosslinking agent (c).
 17. Compositions according to any one of claims1 to 15, characterized in that the binder comprises from 45 to 78% byweight of amorphous polyester (a), from 18 to 30% by weight ofsemicrystalline polyester (b) and 4 to 25% by weight of crosslinkingagent (c).
 18. Varnishes and paints obtained from the thermosettingpowder compositions according to any one of claims 1 to
 17. 19. Processfor obtaining a low-gloss coating on an article, characterized in that athermosetting powder coating composition according to any one of claims1 to 17 is applied to the said article and in that the article thuscoated is cured at a temperature of 140 to 200° C. for a time which maybe as long as 30 minutes.
 20. Satin and matt coatings obtained fromthermosetting powder compositions according to any one of claims 1 to17.
 21. Articles entirely or partially coated using the processaccording to claim 19.